This application is based on Japanese Patent Application No. 2002-93927 filed on Mar. 29, 2002, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a pressure sensor including a sensor element that is disposed in a case having terminals for electrically connecting the sensor element to an outside. More particularly, the pressure sensor includes a capacitor for improving resistance to electromagnetic compatibility (EMC).
2. Related Art
A pressure sensor described in JP-A-7-243926 includes a sensor element for detecting a pressure, and a case for accommodating the sensor element. The case has therein plural terminals for electrically connecting the sensor element to an outside. However, in the pressure sensor, noise electrical current is readily applied to the sensor element due to irradiation of an electromagnetic wave, and the sensor element performs an error operation. That is, the resistance to the EMC is reduced.
To overcome this problem, a capacitor for restricting the noise current is generally assembled to a circuit of a semiconductor chip for constructing the sensor element. However, in this case, the size of the sensor element with the capacitor is increased for improving the restricting effect of the noise current.
On the other hand, the capacitor for releasing the noise current may be disposed at a position except for the capacitor. For example, as shown in FIG. 10, terminals 200 are insert-molded to be embedded and fixed in a case 100 while the case 100 is integrally molded by using resin. The terminals 200 protrude to one end side in the case 100, at a position in a connector portion 110 of the case 100. The connector portion 110 has therein a hollow portion, and protrusion top ends of the terminals 200 are electrically connected to an outside through the connector portion 110. A sensor element (not shown) is mounted on the other end side in the case 100, and is electrically connected to the terminals 200 by wire-bonding.
Further, branch portions 210 branched from the terminals 200 are provided in the case 100. A capacitor 300 is provided at a portion where the branch portions 210 are exposed from the one end side of the case 100, so that the terminals 200 are electrically connected. The capacitor 300 is closed by a potting resin 400 to be sealed therein. However, in the pressure sensor, a diameter D1xe2x80x2 of one end surface of the case 100, for mounting the capacitor 300, is smaller than an inner diameter D2xe2x80x2 of the connector portion 110. Accordingly, when the capacity of the capacitor 300 is increased in order to improve the resistance to EMC, the capacitor 300 is difficult to be mounted. Generally, the size and the shape of the connector portion 110 are liminated for connecting with an outside connector. Thus, in the integrally molded case 100, it is difficult to increase the capacitor mounting area independently from the connector portion 110.
In view of the above-described problems, it is an object of the present invention to provide a pressure sensor that includes a sensor element and a case having therein a terminal for connecting the sensor element to an outside. In the pressure sensor, a capacitor having a large capacity is readily suitably assembled to the case.
It is another object of the present invention to provide a method for manufacturing the pressure sensor.
According to the present invention, a pressure sensor includes a first case having a first surface and a second surface opposite to the first surface, a sensor element disposed in the first case on a side of the first surface for detecting pressure, a terminal embedded in the first case to be fixed in the first case, a second case having an inner wall surface defining an approximate cylindrical hollow portion, and a capacitor for restricting a noise current applied to the sensor element. The second case is bonded to the first case to have a cover surface that cover at least a part of the second surface of the first case, and the terminal is electrically connected to the sensor element and an outside. Further, the terminal includes an extending portion extending in an axial direction in which the first case and the second case are connected, and the extending portion of the terminal protrudes from the second surface of the first case into the hollow portion of the second case in the axial direction to have a protrusion end being electrically connected to the outside. In addition, the terminal includes a branch portion branched from the extending portion and embedded in the first case, a part of the branch portion is exposed to the second surface to form an exposed portion, and the capacitor is disposed on the exposed portion to be electrically connected to the exposed portion. In the pressure sensor, the second surface in the first case has a radial dimension that is larger than a radial dimension of the hollow portion at a predetermined position where the top end of the extending portion of the terminal is positioned. Because the second surface of the first case is used as an actual mounting surface for mounting the capacitor, the capacitor having a large capacity (size) can be readily suitably disposed in the pressure sensor.
Alternatively, at least a part of the exposed portion is positioned at a radial outside of the radial dimension of the hollow portion at the predetermined position. Therefore, the actual mounting surface for mounting the capacitor can be readily provided, regardless of the shape or the size of the hollow portion of the second case.
According to the present invention, by assembling the first and second cases, the second surface of the first case, which is used as an actual mounting surface for mounting the capacitor, can be formed separately from the hollow portion of the second case, which is used as a connector portion. Therefore, the second surface of the first case can be readily formed larger regardless of the size or the shape of the second case with the connector portion. Thus, it is possible to form the radial dimension of the second surface of the first case to be larger than the radial dimension of the hollow portion of the second case at the predetermined position, and it is also possible for at least a part of the exposed portion to be positioned radial outside of the radial dimension of the hollow portion at the predetermined position. As a result, in the pressure sensor, the second surface of the first case can be independently suitably set regardless of the size and the shape of the second case with the connector portion. Therefore, the capacity of the capacitor can be readily suitably changed in accordance with a necessity.